Interstellar flight
Geoffrey A. Landis
Science) in Boston, I presented a review of possible propulsion
technologies for interstellar flight, as part of a symposium that
brought together rocket scientists, anthropologists, linguists, and
science fiction writers* to talk about interstellar travel. The
symposium got quite a lot of publicity (mostly of the gosh wow variety,
and much of it emphasizing some very minor points), including:
On the BBC Web site:
http://news.bbc.co.uk/low/english/in_depth/sci_tech/2002/boston_2002/newsid_1823000/1823822.stm
Discussion on BBC:
http://news.bbc.co.uk/hi/english/talking_point/newsid_1823000/1823990.stm
(I'll also be on the Tony James Breakfast show tomorrow, BBC radio 95.7
in Cambridge [England]).
UPI: http://www.upi.com/view.cfm?StoryID=15022002-031305-7895r
Newspapers:
http://www.nationalpost.com/tech/story.html?f=/stories/20020216/76013.html
http://www.knoxnews.com/kns/sci_and_tech/article/0,1406,KNS_328_991074,00.html
http://www.guardian.co.uk/medicine/story/0,11381,651199,00.html
http://www.nature.com/nsu/020218/020218-4.html
http://www.cosmiverse.com/space02180206.html
and even in a blog:
http://bcmonkey.blogspot.com/
and finally, in Portuguese: http://lanceirolivre.blogspot.com/
It also made the USA Today on Monday (Feb. 18, page 12b).
--
Geoffrey A. Landis
http://www.sff.net/people/geoffrey.landis
Jason Goodman
> At the recent AAAS meeting (American Association for Advancement of
> Science) in Boston, I presented a review of possible propulsion
> technologies for interstellar flight, as part of a symposium that
> brought together rocket scientists, anthropologists, linguists, and
> science fiction writers* to talk about interstellar travel.
Are the visual aids / notes online?
James Stokes
that they were taking up a one-way ticket and would most probably never live
to see the ship's final destination."
These articles are flawed in a number in ways.
It is quite possible that we may discover a cure to aging itself, by way of
genetic manipulation or nanotechnology, thus rendering multi-generation
spacecraft irrelevant.
There is little point sending a spacecraft to a nearby star system unless we
can achieve a high fraction of the speed of light. For example, a spaceship
launched at say 10% light speed will arrive at Alpha Centauri only to find
that it has been over-taken and established by colonists travelling at say
50% light speed.
Decelerating a relativistic spacecraft wouldn't take hundreds of years.
Space-hardened nanomachines could be sent ahead to build a deceleration
laser using asteroidal debris. The same laser or particle beam could be
used to send the crew back home, making roundtrip interstellar missions a
possibility.
"Geoffrey A. Landis" <geoffre...@sff.net> wrote in message
news:3C75055C...@sff.net...
Arian Hokin
> At the recent AAAS meeting (American Association for Advancement of
> Science) in Boston, I presented a review of possible propulsion
> technologies for interstellar flight, as part of a symposium that
> brought together rocket scientists, anthropologists, linguists, and
> science fiction writers* to talk about interstellar travel.
I heard a report about it today on "The Science Show", broadcast on
Radio National here in Aus.
When I heard Robyn Williams (no, not *that* one, the Australian
science broadcaster) reporting the words of one Geoffrey Landis, I
said to meself, "Hey, I read a newsgroup that he posts to." It
certainly sounded very interesting.
Arian
Erik Max Francis
> There is little point sending a spacecraft to a nearby star system
> unless we
> can achieve a high fraction of the speed of light. For example, a
> spaceship
> launched at say 10% light speed will arrive at Alpha Centauri only to
> find
> that it has been over-taken and established by colonists travelling at
> say
> 50% light speed.
This is a common theme in science fiction, but it isn't very realistic.
Travel at 10% is manageable, but hard. Travel at 50% is extremely,
amazingly difficult. Travel at 90% is so flipping hard it's almost out
of the question, even for a type II civilization.
--
Erik Max Francis / m...@alcyone.com / http://www.alcyone.com/max/
__ San Jose, CA, US / 37 20 N 121 53 W / ICQ16063900 / &tSftDotIotE
/ \ Laws are silent in time of war.
\__/ Cicero
Esperanto reference / http://www.alcyone.com/max/lang/esperanto/
An Esperanto reference for English speakers.
Johnny1A
> James Stokes wrote:
>
> > There is little point sending a spacecraft to a nearby star system
> > unless we
> > can achieve a high fraction of the speed of light. For example, a
> > spaceship
> > launched at say 10% light speed will arrive at Alpha Centauri only to
> > find
> > that it has been over-taken and established by colonists travelling at
> > say
> > 50% light speed.
>
> This is a common theme in science fiction, but it isn't very realistic.
> Travel at 10% is manageable, but hard. Travel at 50% is extremely,
> amazingly difficult. Travel at 90% is so flipping hard it's almost out
> of the question, even for a type II civilization.
Why would it be so hard for a K II civilization?
Shermanlee
Geoffrey A. Landis
ships, and the session organizers said that these weren't necessarily
linked, the interstellar flight part didn't ahve to assume
multi-generational ships. For the most part my piece of it was on the
interstellar flight part, not the multi-generational space ship part,
but most of the news coverage had the opposite emphasis-- the reporters
seemed to think that multi-generational spaceships made a really cool story.
Gerry Quinn
>There is little point sending a spacecraft to a nearby star system unless we
>can achieve a high fraction of the speed of light. For example, a spaceship
>launched at say 10% light speed will arrive at Alpha Centauri only to find
>that it has been over-taken and established by colonists travelling at say
>50% light speed.
Why? We can probably make a fission engine that will go at a few
percent of light speed, but we have no notion as to whether fusion or
antimatter will be economically practicable in comparioson, even in a
thousand years.
Fission is *simple*. We can imagine a big dirty fission-powered
ion-drive, built to last. Any tokamak-style fusion engine will be far
more delicate. Antimatter may be always too expensive.
And the first spacecraft won't carry colonists, unless you count
machines.
- Gerry Quinn
Henry Spencer
Erik Max Francis <m...@alcyone.com> wrote:
>> ...it has been over-taken and established by colonists travelling at
>> say 50% light speed.
>
>This is a common theme in science fiction, but it isn't very realistic.
>Travel at 10% is manageable, but hard. Travel at 50% is extremely,
>amazingly difficult. Travel at 90% is so flipping hard it's almost out
>of the question, even for a type II civilization.
We quite routinely do things which our forefathers would have dismissed in
similar terms. You are making a standard error: assuming that all really
drastic changes have already occurred, so the future will be just a matter
of incremental improvements on what we have now. This is a common belief,
but has repeatedly proven completely wrong.
The fundamental limits on (sublight!) travel speed are set -- so far as we
know! -- by energy supply. Yes, reaching 0.5c with a *rocket* is somewhat
difficult, but you don't have to use rockets. At those energies, beamed
power becomes attractive, because then the energy source doesn't have to
come along.
The kinetic energy of a vehicle at 0.5c is up in the exajoules (exa=10^18)
per ton, and this may sound large, but an exajoule is a few years' output
from one of our biggest power plants. That is, you can buy energy on that
scale today, although it's costly. Sources of that size are not (now)
mobile, but with beamed power that is not a fundamental problem.
So the case against 0.5c travel is *already* looking weak... and 0.9c is
only about one order of magnitude harder. Not that we can do either one
today at a practical cost, mind you, but the notion that such speeds are
forever closed to us is clearly unsound.
--
Many things changed on Sept. 11, but the | Henry Spencer he...@spsystems.net
importance of freedom did not. -SpaceNews| (aka he...@zoo.toronto.edu)
lal_truckee
> Decelerating a relativistic spacecraft wouldn't take hundreds of years.
> Space-hardened nanomachines could be sent ahead to build a deceleration
> laser using asteroidal debris. The same laser or particle beam could be
> used to send the crew back home, making roundtrip interstellar missions a
> possibility.
>
If you postulate von Neuman machines, all bets are off - just have
them build a nursery, au pair-bots, manufacture a bit of DNA, and
you're done.
Of course, the Fermi paradox comes roaring back ...
--------------------------------------------------------
Where the hell is everybody?
Enrico
Geoffrey A. Landis
Gerry Quinn wrote:
>
> Why? We can probably make a fission engine that will go at a few
> percent of light speed,
No, fission really isn't good enough for interstellar travel-- you
really do want fusion.
You might be able to get 5000 seconds of specific impulse out of a
fission rocket-- 7000 if you push it hard. Call it an exhaust velocity
of 70 km/sec. If you want to get up to, say 1% of the speed of light,
you need a mass ratio of
mf/mi = exp(-(.01)(300,000)/(70)) = e(-42.8)
Which is 2.5 times ten to the minus 19th: one gram of payload would
require four trillion tons of fuel.
Nuclear electric will do better, but you are now limited by the thrust
level to a tiny fraction of one G; and it will take a very long thrust
duration to get to any reasonable faction of c-- and your mass ratio
will still be very high, since the efficiency of fission just isn't all
that good.
You really do want fusion, or better, if you can get it.
Henry Spencer
Gerry Quinn <ger...@indigo.ie> wrote:
>...We can probably make a fission engine that will go at a few
>percent of light speed...
>Fission is *simple*. We can imagine a big dirty fission-powered
>ion-drive, built to last.
Fission-powered ion simply isn't good enough, even for a few percent of c.
1% of c is 3000 km/s, that is, 3 000 000 m/s. To achieve a few percent of
c with a sane mass ratio, you need rocket Isp on the order of 500 000 s.
Ion rockets just don't go that high, unless you are postulating an ion-
rocket technology radically difficult from what we can build today.
Remember, also, that you need substantial thrust -- not something that ion
rockets specialize in -- if you are to reach such cruising velocities in
a reasonable length of time. A velocity which gets you to Alpha Centauri
in a century isn't useful if you have to spend a thousand years accelerating
first. Even a few percent of c requires a *lot* of accelerating.
Oh, and remember that fission reactors, especially lightweight ones, do
exhaust their fuel. Their working life can't be treated as infinite when
the mission times stretch into decades.
Michael Grosberg
> that they were taking up a one-way ticket and would most probably never live
> to see the ship's final destination."
Do you think anyone would actually volounteer for such a mission? And
even if they did, I suspect the next generation would turn the ship
back to earth the first chance they got.
Frank D Shannon
> In article <3C799AB7...@alcyone.com>,
> Erik Max Francis <m...@alcyone.com> wrote:
> >> ...it has been over-taken and established by colonists travelling at
> >> say 50% light speed.
> >
> >This is a common theme in science fiction, but it isn't very realistic.
> >Travel at 10% is manageable, but hard. Travel at 50% is extremely,
> >amazingly difficult. Travel at 90% is so flipping hard it's almost out
> >of the question, even for a type II civilization.
>
> We quite routinely do things which our forefathers would have dismissed in
> similar terms. You are making a standard error: assuming that all really
> drastic changes have already occurred, so the future will be just a matter
> of incremental improvements on what we have now. This is a common belief,
> but has repeatedly proven completely wrong.
>
True in general.
> The fundamental limits on (sublight!) travel speed are set -- so far as we
> know! -- by energy supply. Yes, reaching 0.5c with a *rocket* is somewhat
> difficult, but you don't have to use rockets. At those energies, beamed
> power becomes attractive, because then the energy source doesn't have to
> come along.
ok
> The kinetic energy of a vehicle at 0.5c is up in the exajoules (exa=10^18)
> per ton, and this may sound large, but an exajoule is a few years' output
> from one of our biggest power plants. That is, you can buy energy on that
> scale today, although it's costly. Sources of that size are not (now)
> mobile, but with beamed power that is not a fundamental problem.
ok
> So the case against 0.5c travel is *already* looking weak... and 0.9c is
> only about one order of magnitude harder. Not that we can do either one
> today at a practical cost, mind you, but the notion that such speeds are
> forever closed to us is clearly unsound.
I think a big problem with travelling at relativistic speeds is sheilding
the ship from relativistic space junk. At .9c a one pound rock in the path
of the spacecraft will destroy it basicly no matter what you sheild it with
or how much sheilding you have. You might have to get unlucky to find that
rock but even if you turn it into vapor at 1,000 miles I think its going to
be trouble.
I know folks here didn't like Earth but Brin had a point when he said we needed
fundamentally new ways of tampering with the universe (IIRC modalities?)
I hope you are right and force fields or something turn up.
Frank
John Schilling
>>There is little point sending a spacecraft to a nearby star system unless we
>>can achieve a high fraction of the speed of light. For example, a spaceship
>>launched at say 10% light speed will arrive at Alpha Centauri only to find
>>that it has been over-taken and established by colonists travelling at say
>>50% light speed.
Right idea, wrong numbers. The 0.1c starship will reach Alpha Centauri in
43 years, the 0.5c starship will require 9 years. Unless the capability
for 0.5c starflight is developed *and implemented* within 34 years of the
0.1c version, the first ship will not be overtaken.
It is rare for technology, especially brute-force technology such as
transportation, to advance at such a rate. Even less common for such
advances to come by surprise; technological development in a particular
field over a single human generation is usually fairly predictable.
At the generation ship level, though, you are correct. Barring some
sort of evacuate-the-dying-Earth scenario, it is probably unwise to
launch any starship that will take more than 50-100 years to reach
a nearby star. On that timescale, you probably will be overtaken by
the people you left behind.
--
*John Schilling * "Anything worth doing, *
*Member:AIAA,NRA,ACLU,SAS,LP * is worth doing for money" *
*Chief Scientist & General Partner * -13th Rule of Acquisition *
*White Elephant Research, LLC * "There is no substitute *
*schi...@spock.usc.edu * for success" *
*661-951-9107 or 661-275-6795 * -58th Rule of Acquisition *
Ray
"Michael Grosberg" <preac...@hotmail.com> wrote in message
news:c21d3ba0.02022...@posting.google.com...
Why would they do that? Ship life would be all they know. They probably
wouldn't have a real hankerin' for living on a dirty planet.
Besides, turning around wouldn't be an option. If you are on your way, the
fuel tanks will probably be about half full. Using it all would cancel out
your velocity - somewhere between stars.
Ray Drouillard
Graham Cowan
Frank D Shannon included:
>
>
> ... I think a big problem with travelling at relativistic speeds
> is sheilding the ship from relativistic space junk. At .9c a
> one pound rock in the path of the spacecraft will destroy it
> basicly no matter what you sheild it with or how much sheilding
> you have. You might have to get unlucky to find that rock but
> even if you turn it into vapor at 1,000 miles I think its going
> to be trouble.
There seem to be things one can do.
(1) Station thin sheets of matter tens of thousands of km
forward. The rock will make a rock-sized hole, or maybe
a little bigger, in the leading foil. It, and the part
of the foil it punched out, will have so expanded
by the time the second foil arrives that
they will mostly miss that foil.
(2) Use laser light sail propulsion, and a beam significantly
wider than the light sail. This and the first thing
work together: by keeping in the middle of the beam,
the foils keep themselves accurately in train with each
other and the vehicle following them, and if crosswinds
aren't too bad the whole train is in an extra high-vacuum
tunnel through interstellar space.
--- Graham Cowan
http://www.eagle.ca/~gcowan/boron_blast.html --
let the baby play with matches in the fuel storage room!
Joann Evans
>
> "James Stokes" <dk...@bigpond.net.au> wrote in message news:<WsFd8.910$RV3....@news-server.bigpond.net.au>...
> > "the 200 or so volunteers who went on such a mission would have to realise
> > that they were taking up a one-way ticket and would most probably never live
> > to see the ship's final destination."
Generation travel's not my favorite way to go, either, but not for
lack of volunteers. I'm sure you'd find aplenty....
> Do you think anyone would actually volounteer for such a mission? And
> even if they did, I suspect the next generation would turn the ship
> back to earth the first chance they got.
Why, necessairily? Those born there don't 'know what they're
missing,' so to speak. Even the volunteers probably come, not directly
from Earth, but from planetary surface, and free-fall space colonies
that aren't *too* different from this starship.
The real difference is that they can never really leave it until the
end of the voyage. (Yes, they can go ouitside when the ship's not under
acceleration, but to where?) In the solar system, it would, by then, be
easy to travel to other colonies and planetary surfaces.
But after several generations of shipboard travel (assuming they stay
socially functional...that's my problem), I can't help wondering how
well they'd *re*adapt to what we consider normal life within a solar
system...
BC
John Schilling wrote:
> >In article <WsFd8.910$RV3....@news-server.bigpond.net.au>, "James Stokes" <dk...@bigpond.net.au> wrote:
>
> >>There is little point sending a spacecraft to a nearby star system unless we
> >>can achieve a high fraction of the speed of light. For example, a spaceship
> >>launched at say 10% light speed will arrive at Alpha Centauri only to find
> >>that it has been over-taken and established by colonists travelling at say
> >>50% light speed.
>
> Right idea, wrong numbers. The 0.1c starship will reach Alpha Centauri in
> 43 years, the 0.5c starship will require 9 years. Unless the capability
> for 0.5c starflight is developed *and implemented* within 34 years of the
> 0.1c version, the first ship will not be overtaken.
Is this assuming instant acceleration to .1 C and .5 C? I would suggest the velocity over interstellar
distances be the average for the distance. Therefore to achieve the times you calculate, if you figure in
acceleration, coasting time, and deceleration times, you end up with the vehicle itself needing a higher
coast or peak velocity than the average over the distance.
Try this, what would a 1 meter/sec^2 acceleration capability achieve? How long to reach peak speed and
destination? How long would you have to accelerate at this rate to achieve your numbers? If 1 m/s^2
acceleration/deceleration isn't enough, please substitute what will make it work to achieve your flight
times.
BC
Paul F. Dietz
> Fission-powered ion simply isn't good enough, even for a few percent of c.
> 1% of c is 3000 km/s, that is, 3 000 000 m/s. To achieve a few percent of
> c with a sane mass ratio, you need rocket Isp on the order of 500 000 s.
> Ion rockets just don't go that high, unless you are postulating an ion-
> rocket technology radically difficult from what we can build today.
If you are ejecting fission product nuclei (which you'd probably
want to do) at 1% c their energy would be roughly 6 MeV. Some sort
of particle accelerator might be appropriate (superconducting
linac?) The ship would probably want to separate the fission
products by element, or even by isotope, and run them through the
engine one after the other, varying the frequency for different
ions.
It would be better if you could eject the fission products directly,
as with the Am-242m fission product rocket concept. One could
also use an isotope like Cm-250 that decays predominantly
by spontaneous fission (halflife 9700 years, though) to avoid
the need to sustain a chain reaction in very thin fuel elements.
Cf-254 could also be used (halflife ~60 days). It's a pity
there's no isotope that decays by SF with a halflife of, say,
100 years.
Paul
George William Herbert
>John Schilling wrote:
>>"James Stokes" <dk...@bigpond.net.au> wrote:
>> >>There is little point sending a spacecraft to a nearby star system
>> >>unless we can achieve a high fraction of the speed of light.
>> >> For example, a spaceship launched at say 10% light speed will
>> >>arrive at Alpha Centauri only to find that it has been over-taken
>> >>and established by colonists travelling at say 50% light speed.
>>
>> Right idea, wrong numbers. The 0.1c starship will reach Alpha Centauri in
>> 43 years, the 0.5c starship will require 9 years. Unless the capability
>> for 0.5c starflight is developed *and implemented* within 34 years of the
>> 0.1c version, the first ship will not be overtaken.
>
>Is this assuming instant acceleration to .1 C and .5 C? I would
>suggest the velocity over interstellar distances be the average
>for the distance. Therefore to achieve the times you calculate,
>if you figure in acceleration, coasting time, and deceleration
>times, you end up with the vehicle itself needing a higher coast
>or peak velocity than the average over the distance.
None of the really credible nearterm interstellar propulsion
methods take that long to accelerate; they're basically all
boost-cruise concepts (laser lightsail, multistage fusion rocket,
antimatter rocket, etc).
What the technology development, energy development, and such suggest
is that if the rate of increase of capability is ever such that it
appears that your ship will be caught by a ship launched in the future
when it's easy and cheap to do so, you should hold off launching now.
However, in general terms the rate of increase of available energy
is predictable, and as John points out, it has to increase pretty
fast for you to achive that criterion. It takes 25 times as much
energy to achive 0.5C as 0.1C, so you need something on the order
of a 25-fold increase in available energy in 34 years, or 9.9%
annual growth if I worked it out right.
-george william herbert
gher...@retro.com
Henry Spencer
Frank D Shannon <shannon...@msn.com> wrote:
>> So the case against 0.5c travel is *already* looking weak... and 0.9c is
>
>I think a big problem with travelling at relativistic speeds is sheilding
>the ship from relativistic space junk. At .9c a one pound rock in the path
>of the spacecraft will destroy it basicly no matter what you sheild it with
Such rocks, fortunately, are distinctly rare out there. Moreover, beyond
a certain (comparatively low) speed, it does not matter a whole lot how
fast you are moving: you sweep out the same volume of space regardless,
and any macroscopic piece of debris is lethal at speeds much lower than
0.9c.
To the extent that this concerns you -- it's not clear that it is worth
any great worry, compared to risks like propulsion failure -- the answer
is basically the same one used to deal with space junk today: you put a
"bumper" out front to vaporize it a safe distance ahead, so what hits you
is gas and maybe very small fragments. Only the scale changes: at 0.9c
you want the bumper to be very thin (so it can be large) and very far
ahead. Think of the ship being preceded by a cloud of dust, replaced
occasionally as exploding bits of junk blow holes in it.
>You might have to get unlucky to find that
>rock but even if you turn it into vapor at 1,000 miles I think its going to
>be trouble.
Then turn it into vapor at 10,000 miles. Or 100,000 miles. This is not
some dreadful bogeyman that inherently cripples any attempt to build a
relativistic starship; it's merely a problem, to be dealt with as part of
the design engineering.
>I know folks here didn't like Earth but Brin had a point when he said we needed
>fundamentally new ways of tampering with the universe (IIRC modalities?)
It certainly would be useful. But we can cope, if we must, without such
magic. It would help, but we don't *need* it.
James Stokes
> > Travel at 10% is manageable, but hard. Travel at 50% is extremely,
> > amazingly difficult. Travel at 90% is so flipping hard it's almost out
> > of the question, even for a type II civilization.
>
> Why would it be so hard for a K II civilization?
>
> Shermanlee
A 1000mT spacecraft travelling at c/2 will have a kinetic energy of
1.125*10^22 joules.
9.24 kilowatts falls on 1 square meter at Mercury orbit.
So assuming that we can reflect this energy with near perfect efficiency,
and that the spacecraft accelerates over a period of 1 year; 39,000 km^2 of
collecting area would be required.
If the sail material has an average areal density of 0.01g/m^2 then the
assembly will mass around 390mT (or 3 Saturn V launches).
David Johnston
>
> In article <3C799AB7...@alcyone.com>,
> Erik Max Francis <m...@alcyone.com> wrote:
> >> ...it has been over-taken and established by colonists travelling at
> >> say 50% light speed.
> >
> >This is a common theme in science fiction, but it isn't very realistic.
> >Travel at 10% is manageable, but hard. Travel at 50% is extremely,
> >amazingly difficult. Travel at 90% is so flipping hard it's almost out
> >of the question, even for a type II civilization.
>
> We quite routinely do things which our forefathers would have dismissed in
> similar terms. You are making a standard error: assuming that all really
> drastic changes have already occurred, so the future will be just a matter
> of incremental improvements on what we have now. This is a common belief,
> but has repeatedly proven completely wrong.
>
It doesn't matter.
Suppose, just for the sake of argument that we launch a colonization ship,
the Slowpoke, that will take, say, 80 years to reach its destination.
This is possible because the human lifespan is now something like 160.
Suppose that 40 years after we launch, we suddenly and unexpectedly
invent the Van Gelbart Pixiedust drive that moves 10 times as fast.
Given that it will likely take at least a few years to build the
Pixiedust I, a ship that will take 8 years to reach the same
destination will still arrive, say, 30 years before the Slowpoke arrives.
So what? The Slowpoke will still arrive to pioneer a new world. In 30 years
the Pixiedust colony will be barely getting started. Even if it arrived a
century early, it would STILL be just barely getting started.
BernardZ
dk...@bigpond.net.au says...
Why would you need such a big ship. It could be tiny.
What excites me the idea that people could live in this ship in a
computer!
David Allsopp
<geoffre...@sff.net> writes
>
>Gerry Quinn wrote:
>>
>> Why? We can probably make a fission engine that will go at a few
>> percent of light speed,
>
>No, fission really isn't good enough for interstellar travel-- you
>really do want fusion.
>You really do want fusion, or better, if you can get it.
>
I recall seeing a comment by some space type saying that what we
*really* need is a way to make a spaceship behave like a submarine.
A sub moves in a medium, and just needs energy to push against the
medium to make itself move. A physics breakthrough that allows us to
(say) push against the quantum vacuum would give us a NAFAL drive
immediately. This is, of course, a reactionless drive but hey, one of
the groups is rasfw...
--
David Allsopp Houston, this is Tranquillity Base.
Remove SPAM to email me The Eagle has landed.
Robert Lynn
Once you have used a quarter of your fuel in accelerating your only
choice is to keep going to your destination as you don't have enough
fuel left to stop, accelerate back towards your start point, and stop
when you get there. It is unlikely that after the first year or two of
flight that you could turn back.
Robert Lynn
>
> In article <Rese8.3600$W8.2...@news.indigo.ie>,
> Gerry Quinn <ger...@indigo.ie> wrote:
> >...We can probably make a fission engine that will go at a few
> >percent of light speed...
> >Fission is *simple*. We can imagine a big dirty fission-powered
> >ion-drive, built to last.
>
> Fission-powered ion simply isn't good enough, even for a few percent of c.
> 1% of c is 3000 km/s, that is, 3 000 000 m/s. To achieve a few percent of
> c with a sane mass ratio, you need rocket Isp on the order of 500 000 s.
> Ion rockets just don't go that high, unless you are postulating an ion-
> rocket technology radically difficult from what we can build today.
>
> Remember, also, that you need substantial thrust -- not something that ion
> rockets specialize in -- if you are to reach such cruising velocities in
> a reasonable length of time. A velocity which gets you to Alpha Centauri
> in a century isn't useful if you have to spend a thousand years accelerating
> first. Even a few percent of c requires a *lot* of accelerating.
IIRC Magnetic Oriion powered by fusion bombs can yield Isps of a few
hundred thousand seconds, and the bigger the ship is the bigger and more
efficient the bombs get. Oriion also provides fast accelerations, 1g
sustained is quite feasible. Apart from beamed power systems they are
currently the only realistic option for interstellar travel, and they
are feasible with the level of technology we have in hand today.
Robert Lynn
mT is pretty confusing. In SI it is milli Tesla - a magnetic flux
density about 10 times that of the earths magnetic field. It could also
be a metre Tesla which makes no sense in the context. milli Tonne? = 1
kg. Mega tonne? = 1000000 tonnes. It seems that you probably mean
metric tonne. In this forum I would forget the 'metric' best to stick
to standard abreviations like kg or Tonnes or lbs.
Geoffrey A. Landis
>
> Do you think anyone would actually volounteer for such a mission?
There are six billion people on the planet. If even one percent
volunteered, the six hundred million volunteers would be an adequate
pool to choose a crew of 200 from, I think.
> And even if they did, I suspect the next generation would turn the ship
> back to earth the first chance they got.
Why should they? The ship would be their home.
I also note that for the types of ships discussed, the process of
stopping, reacclerating backwards, and stopping again at the Earth, is
not very feasible.
Geoffrey A. Landis
> >Try this, what would a 1 meter/sec^2 acceleration capability achieve? How long to reach peak speed and
> >destination? How long would you have to accelerate at this rate to achieve your numbers?
At 10 meters/sec^2 (1 G), you reach 10% of c in 1/10 of a year.
At 1 meters/sec^2 (0.1 G), you reach 10% of c in 1 year.
George William Herbert wrote:
>
> None of the really credible nearterm interstellar propulsion
> methods take that long to accelerate; they're basically all
> boost-cruise concepts (laser lightsail, multistage fusion rocket,
> antimatter rocket, etc).
Actually, ships of the size for a colonization mission might very well
accelerate slowly. It's pretty easy (well, as mega-engineering goes,
"easy") to get a small probe to high accelerations, but the big ships
may not be able to be pushed so hard. A lot of concepts you can come up
with can barely do a hundredth of a G.
> What the technology development, energy development, and such suggest
> is that if the rate of increase of capability is ever such that it
> appears that your ship will be caught by a ship launched in the future
> when it's easy and cheap to do so, you should hold off launching now.
> However, in general terms the rate of increase of available energy
> is predictable, and as John points out, it has to increase pretty
> fast for you to achive that criterion. It takes 25 times as much
> energy to achive 0.5C as 0.1C, so you need something on the order
> of a 25-fold increase in available energy in 34 years, or 9.9%
> annual growth if I worked it out right.
Jordan179
> This is a common theme in science fiction, but it isn't very realistic.
> Travel at 10% is manageable, but hard. Travel at 50% is extremely,
> amazingly difficult. Travel at 90% is so flipping hard it's almost out
> of the question, even for a type II civilization.
Why, the energy requirements or the shielding requirements?
Sincerely Yours,
Jordan
Jordan179
> I think a big problem with travelling at relativistic speeds is sheilding
> the ship from relativistic space junk. At .9c a one pound rock in the path
> of the spacecraft will destroy it basicly no matter what you sheild it with
> or how much sheilding you have. You might have to get unlucky to find that
> rock but even if you turn it into vapor at 1,000 miles I think its going to
> be trouble.
>
> I know folks here didn't like Earth but Brin had a point when he said we needed
> fundamentally new ways of tampering with the universe (IIRC modalities?)
> I hope you are right and force fields or something turn up.
Energy to generate and the precision to control the "force field" is
the main problem, because we _already_ have the physics (but not the
engineering capability) to build the kind of "force field" needed to
shield a starship. What the ship would have to do is maintain an
active (or VERY good passive) sensor watch on the space immediately in
front of itself, use particle beams to break up debris into
microscopic charged particles, and then use an electromagnetic field
to sweep the debris off a direct collision course. The front of the
starship should also be heavily armored and shielded, because some
particles will make it through anyway.
Could we build this now? No. We can't make sensors that good, energy
beams that nimble or reliable, nor an electromagnetic field generator
of that intensity which would remain stable for years at a time.
Will we be able to build this 100 or 200 years from now? I don't see
why not, as none of this design requires anything forbidden by known
physical law, and over the next century or two I'm SURE we'll find at
least one or two shortcuts.
Then there's the energy required for the trip -- which as others have
pointed out, is vast, but not beyond the (theoretical) capability of
even our own civilization, today, if we were to spend many years
amassing it. And given that as technology advances civilization
commands more and more energy, eventually we will reach a point where
governments, corporations, or even individuals may be able to command
the requisite power.
And then, Man will be off to the stars.
Sincerely Yours,
Jordan
Jordan179
> Michael Grosberg wrote:
> >
> > "James Stokes" <dk...@bigpond.net.au> wrote in message news:<WsFd8.910$RV3....@news-server.bigpond.net.au>...
> > > "the 200 or so volunteers who went on such a mission would have to realise
> > > that they were taking up a one-way ticket and would most probably never live
> > > to see the ship's final destination."
>
> Generation travel's not my favorite way to go, either, but not for
> lack of volunteers. I'm sure you'd find aplenty....
>
> But after several generations of shipboard travel (assuming they stay
> socially functional...that's my problem), I can't help wondering how
> well they'd *re*adapt to what we consider normal life within a solar
> system...
ObSF: "Universe," by Robert Heinlein. Also "Rogue Ship," by A. E. Van Vogt.
Sincerely Yours,
Jordan
Henry Spencer
James Stokes <dk...@bigpond.net.au> wrote:
>> > ...Travel at 90% is so flipping hard it's almost out
>> > of the question, even for a type II civilization.
>> Why would it be so hard for a K II civilization?
>
>1.125*10^22 joules.
Uh, a Kardashev Type II civilization is *defined* as one that can control
roughly the power output of a Sun-type star -- about 10^26W -- for
non-survival purposes. Neglecting engineering details, accelerating that
spacecraft to c/2 requires 0.1% of that civilization's available power for
1/10 of a second.
>9.24 kilowatts falls on 1 square meter at Mercury orbit.
>So assuming that we can reflect this energy with near perfect efficiency,
>and that the spacecraft accelerates over a period of 1 year; 39,000 km^2 of
>collecting area would be required.
>If the sail material has an average areal density of 0.01g/m^2 then the
>assembly will mass around 390mT (or 3 Saturn V launches).
Note that a solar sail imparts, to itself and its payload, only a tiny
fraction of the energy of the light falling on it.
Moreover, you can't stay at Mercury's distance for a year of acceleration,
nor can you beam sunlight to the accelerating sail with a mirror system.
However, you are correct in thinking that obtaining sufficient energy for
high-speed interstellar travel will require quite large collecting areas
for sunlight (that being probably the best source for really large amounts
of energy), such as might be obtained by large-scale automated production
of solar power satellites.
If 10% of the mass of an asteroid 1km in diameter with a density of
2.5t/m^3 (vaguely typical for stone) can be converted to solar arrays with
a mass density of 1g/m^2, that will cover 130 million square kilometers --
about the same cross-section as the Earth -- collecting 1.2 exawatts of
sunlight at Mercury orbit. If we assume 10% efficiency in conversion to
electric power (solar-cell technology chosen for production simplicity
rather than efficiency), and 50% efficiency in conversion to laser light
(today's diode-laser arrays are edging up past 45%), this requires about
2.5 days to deliver 1.125*10^22J as laser light. Conversion of the energy
to propulsion is left as an exercise for the student, but note that with
an acceleration time of a year (we wouldn't want to go a lot lower, that's
about 0.5G), a conversion efficiency of 1% is plenty.
The solar system has *many* 1km asteroids which wouldn't be missed.
Nobody said that this was something we were going to be able to do next
week. The point is that, contrary to the original assertion, there is no
reason to believe that it is fundamentally impossible, and indeed it seems
to require only straightforward (although sizable) extrapolations of
capabilities we already have.
John Schilling
[0.1c starship to Alpha Centauri]
>> >> ...it has been over-taken and established by colonists travelling at
>> >> say 50% light speed.
>It doesn't matter.
>Suppose, just for the sake of argument that we launch a colonization ship,
>the Slowpoke, that will take, say, 80 years to reach its destination.
>This is possible because the human lifespan is now something like 160.
>Suppose that 40 years after we launch, we suddenly and unexpectedly
>invent the Van Gelbart Pixiedust drive that moves 10 times as fast.
>Given that it will likely take at least a few years to build the
>Pixiedust I, a ship that will take 8 years to reach the same
>destination will still arrive, say, 30 years before the Slowpoke arrives.
>So what? The Slowpoke will still arrive to pioneer a new world. In 30 years
>the Pixiedust colony will be barely getting started. Even if it arrived a
>century early, it would STILL be just barely getting started.
It doesn't matter to you that the passengers and crew of the Slowpoke
have needlessly spent 72 years cooped up in a spaceship? Because it
will probably matter to *them*.
Under your scenario, those same people could just as well have looked at
the plans for the Slowpoke, said "we'll wait", spend the next fourty-two
years living in a large, diverse, prosperous (inter)planetary civilization
instead. And *then* embarked on their interstellar expedition, to spend
a mere eight years in transit and begin pioneering their new world with a
technology fourty years more advanced.
It isn't a competition between the Slowpoke colonists and the Pixiedust
colonists. It's a question of whether *any particular* group of colonists
should embark on the Slowpoke or wait for the Pixiedust. If the Pixiedust
is coming, you wait for it.
John Schilling
>BC <bc2...@snet.net> wrote:
>>John Schilling wrote:
>>>"James Stokes" <dk...@bigpond.net.au> wrote:
>>> >>There is little point sending a spacecraft to a nearby star system
>>> >>unless we can achieve a high fraction of the speed of light.
>>> >> For example, a spaceship launched at say 10% light speed will
>>> >>arrive at Alpha Centauri only to find that it has been over-taken
>>> >>and established by colonists travelling at say 50% light speed.
>>> Right idea, wrong numbers. The 0.1c starship will reach Alpha Centauri in
>>> 43 years, the 0.5c starship will require 9 years. Unless the capability
>>> for 0.5c starflight is developed *and implemented* within 34 years of the
>>> 0.1c version, the first ship will not be overtaken.
>>Is this assuming instant acceleration to .1 C and .5 C? I would
>>suggest the velocity over interstellar distances be the average
>>for the distance. Therefore to achieve the times you calculate,
>>if you figure in acceleration, coasting time, and deceleration
>>times, you end up with the vehicle itself needing a higher coast
>>or peak velocity than the average over the distance.
>None of the really credible nearterm interstellar propulsion
>methods take that long to accelerate; they're basically all
>boost-cruise concepts (laser lightsail, multistage fusion rocket,
>antimatter rocket, etc).
Right. I assumed 1 G acceleration, but it changes the timing by
only a year or so if you reduce that to 0.1 G.
>What the technology development, energy development, and such suggest
>is that if the rate of increase of capability is ever such that it
>appears that your ship will be caught by a ship launched in the future
>when it's easy and cheap to do so, you should hold off launching now.
>However, in general terms the rate of increase of available energy
>is predictable, and as John points out, it has to increase pretty
>fast for you to achive that criterion. It takes 25 times as much
>energy to achive 0.5C as 0.1C, so you need something on the order
>of a 25-fold increase in available energy in 34 years, or 9.9%
>annual growth if I worked it out right.
At 0.5c, relativistic effects are not entirely trivial. The 0.5c
starship needs 28.7 times the energy as the 0.1c version, for a
10.4% annual growth rate. Not a big change, of course. Looking
at a broader range of possibilities, a mere 4.7% growth rate still
leaves you in danger of being overtaken by a starship that launches
next year at 0.1025c.
But even 4.7%/year is well above the historical trend for such things.
Not impossible or unprecedented, of course, but also not likely to
catch you by surprise.
A 0.05c starship, OTOH, will be overtaken if the launching civilization
can achieve an energy growth rate of 2.4%, which is quite likely. So
don't launch for Alpha Centauri until you can make at least 0.1c, or
until civilization is about to collapse around you.
Shardrukar
writes:
>Oh, and remember that fission reactors, especially lightweight ones, do
>exhaust their fuel. Their working life can't be treated as infinite when
>the mission times stretch into decades.
Or centuries, but, are you saying that the areas of fission reactor engineering
are past, and that there are no major application design improvements possible
in this area? Space based reactors are essentially as good as they can get? I
didn't think Earth based nuclear power plant design had reached that point yet.
Shardrukar
preac...@hotmail.com (Michael Grosberg) writes:
>Do you think anyone would actually volounteer for such a mission? And
>even if they did, I suspect the next generation would turn the ship
>back to earth the first chance they got.
>
More than could go, and I seriously doubt succeeding generations would. Did you
ask to be born where you were born, did any one, did all the children in your
country flee to other countries as soon as thier parents died. The ship would
be thier home. I think the biggest problem comes at the end of the trip, when
you try to get people who have lived for the last several generations aboard a
ship to abandon it for some harsh alien planetary surface.
Shardrukar
writes:
> The real difference is that they can never really leave it until the
>end of the voyage. (Yes, they can go ouitside when the ship's not under
>acceleration, but to where?) In the solar system, it would, by then, be
>easy to travel to other colonies and planetary surfaces.
>
> But after several generations of shipboard travel (assuming they stay
>socially functional...that's my problem), I can't help wondering how
>well they'd *re*adapt to what we consider normal life within a solar
>system...
>
Good points, one way to alieviate this is to use a colony to spread colonies.
One or several colony habitats travelling at .01c on a course that intersects
colony target systems. I agree that there will probably be some difficulty
getting people used to living on ships/habitats to integrate to system life,
but if the generation ships are basically colonial habitats in the first place
and the initial primary colonies in the target system are orbital habitats then
the transition should be minor.
Shardrukar
<rgo...@telusplanet.net> writes:
>Suppose, just for the sake of argument that we launch a colonization ship,
>the Slowpoke, that will take, say, 80 years to reach its destination.
>This is possible because the human lifespan is now something like 160.
>Suppose that 40 years after we launch, we suddenly and unexpectedly
>invent the Van Gelbart Pixiedust drive that moves 10 times as fast.
>Given that it will likely take at least a few years to build the
>Pixiedust I, a ship that will take 8 years to reach the same
>destination will still arrive, say, 30 years before the Slowpoke arrives.
>
>So what? The Slowpoke will still arrive to pioneer a new world. In 30 years
>the Pixiedust colony will be barely getting started. Even if it arrived a
>century early, it would STILL be just barely getting started.
>
Agreed, and just to harp the point one more time, if you use large orbital
habitats as the interstellar colony seed-ships, then time and speed become much
less relevant. Faster ships later on would merely utilize the slower habitats
as forward bases as the then procede to do initial exploration and
developement, as well as providing a means of re-supplying the slower seed habs
with materials personnel and technology.
Shardrukar
Schilling) writes:
>At the generation ship level, though, you are correct. Barring some
>sort of evacuate-the-dying-Earth scenario, it is probably unwise to
>launch any starship that will take more than 50-100 years to reach
>a nearby star. On that timescale, you probably will be overtaken by
>the people you left behind.
>
This depends a lot upon how you do the spreading in the first place. If you use
self-sufficient habitats as your generational seed ships then this isn't that
big a problem. The ships are colonies in themselves, travelling ever outward
and intersecting target star systems along the way. Colonization per se is
carried out via shorter range craft from the seed ship as it approaches the
target systems. At .01c these seed ship colonies would spend well over a
hundred years within close proximity to the target systems (well within range
for shorter journey .1c+ craft). Faster craft will merely utilize these seed
colonies as port calls, exchanging crews, technology, information etc.,. Newly
established colonies refill the seed ships stores as it passes and then focuses
on growing thier own colony, perhaps launching thier own seed ship colonies
within a century or so.
Shardrukar
>No, fission really isn't good enough for interstellar travel-- you
>really do want fusion.
>
I don't know, though we've pretty well killed the Salt-Water Fission Rocket, it
still has a slight potential, and then there's always micro-fission (even
without the fusion boost-in fact may be easier without the added neutron flux
of the fusion reaction pre-irradating the incoming ICF pellets), but it is
generally considered more of an AM drive due to the usage of the a-Ps to drive
the fission process. And if you're talking about power source for other drive
systems, unless you're going to attach some large mhd unit to your fusion
exhaust plume and run the engine constantly, I don't see how you're going to
get around a fission source.
Walter Bushell
> The symposium was on interstellar flight and multi-generational space
> ships, and the session organizers said that these weren't necessarily
> linked, the interstellar flight part didn't ahve to assume
> multi-generational ships. For the most part my piece of it was on the
> interstellar flight part, not the multi-generational space ship part,
> but most of the news coverage had the opposite emphasis-- the reporters
> seemed to think that multi-generational spaceships made a really cool story.
___>We do not even know is a closed ecology is possible on less than a
planetary scale. 1
Erik Max Francis
> mT is pretty confusing. In SI it is milli Tesla - a magnetic flux
> density about 10 times that of the earths magnetic field. It could
> also
> be a metre Tesla which makes no sense in the context. milli Tonne? =
> 1
> kg. Mega tonne? = 1000000 tonnes. It seems that you probably mean
> metric tonne. In this forum I would forget the 'metric' best to stick
> to standard abreviations like kg or Tonnes or lbs.
In context, it was pretty obvious he meant megatonnes, Mt.
--
Erik Max Francis / m...@alcyone.com / http://www.alcyone.com/max/
__ San Jose, CA, US / 37 20 N 121 53 W / ICQ16063900 / &tSftDotIotE
/ \ Laws are silent in time of war.
\__/ Cicero
Esperanto reference / http://www.alcyone.com/max/lang/esperanto/
An Esperanto reference for English speakers.
David Johnston
> It doesn't matter to you that the passengers and crew of the Slowpoke
> have needlessly spent 72 years cooped up in a spaceship? Because it
> will probably matter to *them*.
>
> Under your scenario, those same people could just as well have looked at
> the plans for the Slowpoke, said "we'll wait", spend the next fourty-two
> years living in a large, diverse, prosperous (inter)planetary civilization
> instead. And *then* embarked on their interstellar expedition, to spend
> a mere eight years in transit and begin pioneering their new world with a
> technology fourty years more advanced.
>
> It isn't a competition between the Slowpoke colonists and the Pixiedust
> colonists. It's a question of whether *any particular* group of colonists
> should embark on the Slowpoke or wait for the Pixiedust. If the Pixiedust
> is coming, you wait for it.
If you foresee the Pixiedust Drive, of course. The odds are of course that
there won't be an unforeseen breakthrough of that magnitude in that short a
timeframe. The prospect that there might be is a gamble of course, but a
much smaller and more innocuous one than the possibility that when the
Slowpoke arrives, there will be some undetected quality about the planet
that will wipe them all out anyway.
Damo
> I know folks here didn't like Earth but Brin had a point when he said we
needed
> fundamentally new ways of tampering with the universe (IIRC modalities?)
> I hope you are right and force fields or something turn up.
>
Hey, so that is the Brin you guys are always talking about. (sorry)
I didnt mind Earth, the ending never seemed right to me but he painted what
I thought to be a very realistic picture of Earth in the mid-21st century.
Except ofcourse for sea level but he admits that in the intro.
Damo
George William Herbert
>Geoffrey A. Landis <geoffre...@sff.net> wrote:
>> The symposium was on interstellar flight and multi-generational space
>> ships, and the session organizers said that these weren't necessarily
>> linked, the interstellar flight part didn't ahve to assume
>> multi-generational ships. For the most part my piece of it was on the
>> interstellar flight part, not the multi-generational space ship part,
>> but most of the news coverage had the opposite emphasis-- the reporters
>> seemed to think that multi-generational spaceships made a really cool story.
>
>planetary scale.
That is not true. Complicated closed ecology systems (Biosphere-2)
have failed to match predictions, but simple ones have operated for
extended periods (year-plus) at NASA and associated research centers
with good success. Websearch on "biological CELSS".
-george william herbert
gher...@retro.com
Hop David
Graham Cowan wrote:
> Frank D Shannon included:
> >
> >
> > ... I think a big problem with travelling at relativistic speeds
> > is sheilding the ship from relativistic space junk. At .9c a
> > one pound rock in the path of the spacecraft will destroy it
> > basicly no matter what you sheild it with or how much sheilding
> > you have. You might have to get unlucky to find that rock but
> > even if you turn it into vapor at 1,000 miles I think its going
> > to be trouble.
>
> There seem to be things one can do.
>
> (1) Station thin sheets of matter tens of thousands of km
> forward. The rock will make a rock-sized hole, or maybe
> a little bigger, in the leading foil. It, and the part
> of the foil it punched out, will have so expanded
> by the time the second foil arrives that
> they will mostly miss that foil.
>
> (2) Use laser light sail propulsion, and a beam significantly
> wider than the light sail. This and the first thing
> work together: by keeping in the middle of the beam,
> the foils keep themselves accurately in train with each
> other and the vehicle following them, and if crosswinds
> aren't too bad the whole train is in an extra high-vacuum
> tunnel through interstellar space.
>
> --- Graham Cowan
> http://www.eagle.ca/~gcowan/boron_blast.html --
> let the baby play with matches in the fuel storage room!
I had a design something like this:
http://clowder.net/hop/gofix/starship.html
but the thin sheets of matter went ahead via chemical rockets. During
acceleration with fusion reactors the sheets be attached to the ship.
But that would hopefully be a small fraction of the journey.
I made the ship long and narrow to minimize its profile.
The thin sheets also had radar sensors & a lasers to blast apart debris.
A current circling through a supercondutor wire along the perimeter
provides a magnetic field to deflect the ions.
Gerry Quinn
>In article <Rese8.3600$W8.2...@news.indigo.ie>,
>Gerry Quinn <ger...@indigo.ie> wrote:
>>...We can probably make a fission engine that will go at a few
>>percent of light speed...
>>Fission is *simple*. We can imagine a big dirty fission-powered
>>ion-drive, built to last.
>
>Fission-powered ion simply isn't good enough, even for a few percent of c.
>1% of c is 3000 km/s, that is, 3 000 000 m/s. To achieve a few percent of
>c with a sane mass ratio, you need rocket Isp on the order of 500 000 s.
>Ion rockets just don't go that high, unless you are postulating an ion-
>rocket technology radically difficult from what we can build today.
Well, I guess I am proposing that. As somebody said, you'd need to be
talking about the equivalent of a particle accelerator. In a sense, you
want to have mostly 'energy' in the exhaust, so to speak.
>Remember, also, that you need substantial thrust -- not something that ion
>rockets specialize in -- if you are to reach such cruising velocities in
>a reasonable length of time. A velocity which gets you to Alpha Centauri
>in a century isn't useful if you have to spend a thousand years accelerating
>first. Even a few percent of c requires a *lot* of accelerating.
This is a valid point.
>Oh, and remember that fission reactors, especially lightweight ones, do
>exhaust their fuel. Their working life can't be treated as infinite when
>the mission times stretch into decades.
In principle, they can be shut down to any desired amount with enough
damping / geometry change. However, I imagine you would design the
reactor to fit them mission, so it was 'on' most of the time.
Still, when I look at the tokamak possibilities, it seems even less
plausible. Tritium won't last, so you have to generate it continuously
from lithium. We're talking lots of moving parts in a radioactive
environment. (Hydrogen bombs blasting a concrete base or the far
side of an asteroid have been suggested, of course...)
Anti-matter is the holy grail - but when you have to make it atom by
atom...
Interstellar flight is not as easy as we tend to think. My personal
bias is to think up something technologically imaginable and see how
long it takes.
- Gerry Quinn
John Savard
Grosberg) wrote, in part:
>Do you think anyone would actually volounteer for such a mission? And
>even if they did, I suspect the next generation would turn the ship
>back to earth the first chance they got.
For one thing, only the next generation's children would make it back
to Earth, since it would take time to lose all that velocity.
For another, that depends on the kind of ship.
Since a generation ship would need to have life support systems that
remain stable for decades, a way of achieving that would be to build
the ship like an O'Neill colony.
That the second generation would hanker for wide open spaces, for the
song of birds in the air, for trees... that makes sense. That they
wouldn't have more of that kind of thing on the ship than most people
do on Earth, though, is what isn't necessarily true.
Of course, lifespan extension would probably come long before sublight
interstellar travel.
Gerry Quinn
>
>Suppose, just for the sake of argument that we launch a colonization ship,
>the Slowpoke, that will take, say, 80 years to reach its destination.
>This is possible because the human lifespan is now something like 160.
>Suppose that 40 years after we launch, we suddenly and unexpectedly
>invent the Van Gelbart Pixiedust drive that moves 10 times as fast.
>Given that it will likely take at least a few years to build the
>Pixiedust I, a ship that will take 8 years to reach the same
>destination will still arrive, say, 30 years before the Slowpoke arrives.
>
>So what? The Slowpoke will still arrive to pioneer a new world. In 30 years
>the Pixiedust colony will be barely getting started. Even if it arrived a
>century early, it would STILL be just barely getting started.
Come to think of it, the 'fast' colonists will have dealt with all the
really nasty skin-eating viruses / telepathic hungry plants, and moved
their base camp away from its original position on the radioactive
volcano / ancient alien graveyard / migration path of the silicon
megabeast...
The Slowpokers will be just in time to take over from the demoralised
survivors of the Pixiedust!
- Gerry Quinn
Henry Spencer
Walter Bushell <pr...@panix.com> wrote:
>> but most of the news coverage had the opposite emphasis-- the reporters
>> seemed to think that multi-generational spaceships made a really cool story.
>
>___>We do not even know is a closed ecology is possible on less than a
>planetary scale. 1
Actually, we do, it's been demonstrated. Some years ago, you could buy
little sealed glass globes, maybe 15cm in diameter, containing plants and
small shrimp. All you had to supply was light. Many of them died off
quickly after being sealed up, and a good many more would eventually
deteriorate in some way or other... but some of them kept going seemingly
indefinitely, through many generations of plants and shrimp. I don't know
if there are any still around.
Making larger systems work well is admittedly hard.
Henry Spencer
Shardrukar <shard...@aol.com> wrote:
>>Oh, and remember that fission reactors, especially lightweight ones, do
>
>Or centuries, but, are you saying that the areas of fission reactor engineering
>are past, and that there are no major application design improvements possible
>in this area?
By no means. But the original suggestion was "well, we can do this now,
and everything else is all speculative". No, we can't do it now, and
while we can probably improve it considerably, that's subject to the same
criticism.
Personally, I like Robert Forward's comment: "antimatter propulsion is
no longer science fiction". (Also: "antimatter is easier than fusion".)
Gordon D. Pusch
> In article <3C7AB71D...@sff.net>, Geoffrey A. Landis
> <geoffre...@sff.net> writes
>>
>> Gerry Quinn wrote:
>>>
>>> Why? We can probably make a fission engine that will go at a few
>>> percent of light speed,
>>
>> No, fission really isn't good enough for interstellar travel-- you
>> really do want fusion.
>> [...interesting calculations snipped...]
>> You really do want fusion, or better, if you can get it.
>>
>
> I recall seeing a comment by some space type saying that what we
> *really* need is a way to make a spaceship behave like a submarine.
> A sub moves in a medium, and just needs energy to push against the
> medium to make itself move. A physics breakthrough that allows us to
> (say) push against the quantum vacuum would give us a NAFAL drive
> immediately. This is, of course, a reactionless drive but hey, one of
> the groups is rasfw...
Such a ``vacuum propeller'' will still require energy to run, because
it cannot consume any less energy than the increase in the kinetic energy
of the ship without violating the First Law of Thermodynamics and allowing
you to construct a perpetual motion machine. Hence, unless you postulate
that energy is not conserved, or that some sort of ``free energy machine''
exists, a ``NAFAL'' drive would still require an enormous on-board
energy-supply to get a ship up to a significant fraction of lightspeed;
for example, to get up to .9 c requires the ship convert at least 84%
of its initial mass into energy (i.e., a mass-ratio of about 5.3) ---
even assuming 100% efficient mass/energy conversion, and a 100% efficient
NAFAL drive. Real ships and drives with less than 100% efficiency would
need to convert an even higher fraction of their mass into energy.
For comparison, a 100% efficient photon drive only needs a mass-ratio
of about 4.4 to get to 0.9 c --- so ironically, it appears that in this case
at least, a ``vacuum propeller'' is actually _LESS_ efficient than a photon
drive !!!
A ``vacuum propeller'' would also requires that an ``aether'' or some other
form of preferred reference-frame must exist for it to ``push against,''
or else it again cannot be any more efficient than a photon drive without
violating the First Law of Thermodynamics and allowing you to construct
a perpetual motion machine. However, the existence of such a preferred
reference-frame requires that Einstein's Principle of Relativity must
be false --- and currently there is absolutely =NO= experimental evidence
that favors an ``aether'' theory over Special Relativity.
So it seems to me that discovering such a ``vacuum propeller'' would by
itself be insufficient to solve the problem of interstellar flight ---
you must also discover a ``free energy machine,'' and show that Einstein's
Special Theory of Relativity is wrong, first.
-- Gordon D. Pusch
perl -e '$_ = "gdpusch\@NO.xnet.SPAM.com\n"; s/NO\.//; s/SPAM\.//; print;'
Del Cotter
>Robert Lynn wrote:
>> mT is pretty confusing. In SI it is milli Tesla - a magnetic flux
>> density about 10 times that of the earths magnetic field. It could
>> be a metre Tesla which makes no sense in the context. milli Tonne? =
>> kg. Mega tonne? = 1000000 tonnes. It seems that you probably mean
>> metric tonne. In this forum I would forget the 'metric' best to stick
>> to standard abreviations like kg or Tonnes or lbs.
>
>In context, it was pretty obvious he meant megatonnes, Mt.
No, look:
On Tue, 26 Feb 2002, in rec.arts.sf.science,
James Stokes <dk...@bigpond.net.au> said:
>A 1000mT spacecraft travelling at c/2 will have a kinetic energy of
>1.125*10^22 joules.
The numbers wouldn't stack up if it were megatonnes. 150*10^6 m s-1 and
1.13*10^22 J implies 1*10^6 kg, not 1*10^12 kg. It has to be metric
tonnes.
--
. . . . Del Cotter d...@branta.demon.co.uk . . . .
JustRead:cLeodCosmonautKeep:JRRTolkienTheFellowshipOfTheRing:ChinaMievil
lePerdidoStreetStation:KatherineBlakeTheInteriorLife:KeithBrookeExpatria
ToRead:CSLewisTheVoyageOfTheDawnTreader:MichaelMarshallSmithOnlyForward:
Joann Evans
> > But after several generations of shipboard travel (assuming they stay
> > socially functional...that's my problem), I can't help wondering how
> > well they'd *re*adapt to what we consider normal life within a solar
> > system...
>
> ObSF: "Universe," by Robert Heinlein. Also "Rogue Ship," by A. E. Van Vogt.
>
> Sincerely Yours,
> Jordan
Exactly the kinds of things I had in mind.....
Henry Spencer
Erik Max Francis <m...@alcyone.com> wrote:
>> mT is pretty confusing...
>
>In context, it was pretty obvious he meant megatonnes, Mt.
Except that the arithmetic came out properly only if he meant metric tons.
PBlase
people who have lived for the last several generations aboard a ship to abandon
it for some harsh alien planetary surface.
Why bother? Once you're up there, it would be easier to stay there and use
space-based materials and energy. Planets are nice places to visit, but not
necessary as living places.
James Stokes
"Erik Max Francis" <m...@alcyone.com> wrote in message
news:3C7C0C79...@alcyone.com...
James Stokes
There is no physical or engineering principle which rules out
nanoassemblers, Drexler proved this in his book "Nanosystems".
A molecular nanotechnology company called Zyvex is working specifically
towards this goal. After winning the $25M NIST ATP contract they expect to
have microscale assemblers using microelectromechanical systems (MEMS) on
the market by 2005. These capabilities will then be expanded to nanometer
geometries, and nanoelectromechanical systems (NEMS) will be developed for
prototype Nanoscale assemblers.
So if everything goes according to plan, we could have fully functional
universal nanoassemblers well before 2020.
The practice of converting asteroids into ultra-large sail reflectors is now
much more realistic, the entire process could be automated thus eliminating
the need for massive space infrastructure.
Rather than focusing powerful lasers on a distant sail, sunlight could be
redirected to a particle beam of microscopic laser sails aka "SailBeam".
These micro-sails would be ionized by a ship-mounted laser and reflected off
a MagSail. This way, you avoid the need for very large optical apertures
which are usually associated with interstellar light sails
Shardrukar
Schilling) writes:
>It isn't a competition between the Slowpoke colonists and the Pixiedust
>colonists. It's a question of whether *any particular* group of colonists
>should embark on the Slowpoke or wait for the Pixiedust. If the Pixiedust
>is coming, you wait for it.
>
Of course, like so many technical revolutions (commercial fusion power comes
easiest to mind), the "pixiedust" drive may be 40 years away for the next
200years. It depends more upon the drive and financing when these coincide the
trips will happen whether it is at .8c or .0001c are the mere technical details
of doing it.
Jason Goodman
> John Schilling wrote:
>
>>It isn't a competition between the Slowpoke colonists and the Pixiedust
>>colonists. It's a question of whether *any particular* group of colonists
>>should embark on the Slowpoke or wait for the Pixiedust. If the Pixiedust
>>is coming, you wait for it.
>>
>
> If you foresee the Pixiedust Drive, of course. The odds are of course that
> there won't be an unforeseen breakthrough of that magnitude in that short a
> timeframe. The prospect that there might be is a gamble of course, but a
> much smaller and more innocuous one than the possibility that when the
> Slowpoke arrives, there will be some undetected quality about the planet
> that will wipe them all out anyway.
Or to put it another way: if you're commuting to work, it's wiser to take
the bus than to sit at home hoping that someone will land a helicopter in
your backyard and offer you a lift.
And there's another factor to consider: you're considering only one possible
destination. If a miracle occurs, and the Pixiedust drive is created, a
smart civilization will send the U.S.S. Pixie off to SOME DIFFERENT STAR
than the destination of the Slowpoke. Unless you can make so many Pixiedust
Drive ships, moving so fast as to completely explore every star system in
range before the Slowpoke arrives, it's silly to waste the effort you've
invested in the Slowpoke when there's lots of other goals to meet. The
Slowpoke crew may lose the privilege of being the first people ever to reach
another star system, but their effort isn't wasted.
Even if the Slowpoke's destination is the only habitable system nearby, you
can send the Pixie off to a star system up to 10 times farther away, in the
same timeframe as the Slowpoke's voyage. The Pixie's longer range gives you
roughly 1000 times as many destinations to choose from.
Hop David
John Savard wrote:
> On 25 Feb 2002 14:55:17 -0800, preac...@hotmail.com (Michael
> Grosberg) wrote, in part:
>
> >Do you think anyone would actually volounteer for such a mission? And
> >even if they did, I suspect the next generation would turn the ship
> >back to earth the first chance they got.
>
> For one thing, only the next generation's children would make it back
> to Earth, since it would take time to lose all that velocity.
>
> For another, that depends on the kind of ship.
>
> Since a generation ship would need to have life support systems that
> remain stable for decades, a way of achieving that would be to build
> the ship like an O'Neill colony.
I can see a cylinder with soil & artificial gravity provided with spin.
But at several lightyears from the nearest star they would need a large
mirror to get enough sunlight.
>
>
> That the second generation would hanker for wide open spaces, for the
> song of birds in the air, for trees... that makes sense. That they
> wouldn't have more of that kind of thing on the ship than most people
> do on Earth, though, is what isn't necessarily true.
>
> Of course, lifespan extension would probably come long before sublight
> interstellar travel.
Our species seems inclined to conflict. Long lifespans wouldn't help if
the ship were wrecked by war. I wonder if it'd be possible to genengineer
a population with lower testosterone levels.
>
>
> John Savard
> http://plaza.powersurfr.com/jsavard/index.html
Nyrath the nearly wise
> Actually, we do, it's been demonstrated. Some years ago, you could buy
> little sealed glass globes, maybe 15cm in diameter, containing plants and
> small shrimp. All you had to supply was light. Many of them died off
> quickly after being sealed up, and a good many more would eventually
> deteriorate in some way or other... but some of them kept going seemingly
> indefinitely, through many generations of plants and shrimp. I don't know
> if there are any still around.
They are still available.
http://www.eco-sphere.com/ecospheres.html
Mark Q
>>A 1000mT spacecraft travelling at c/2 will have a kinetic energy of
>>1.125*10^22 joules.
>
>The numbers wouldn't stack up if it were megatonnes. 150*10^6 m s-1 and
>1.13*10^22 J implies 1*10^6 kg, not 1*10^12 kg. It has to be metric
>tonnes.
K = M(gamma-1)c^2
For 0.5c, gamma = 1.1547
1000mT = 10^12 kg ???
So K = 10^12 * 0.1547 * 9*10^16
= 1.39*10^28 J
By Jove, you're right! :)
Mark Q
Erik Max Francis
> No, actually I meant metric tonne. Note the small 'm'
Well, then shame on you then.
Shardrukar
(PBlase) writes:
>Why bother? Once you're up there, it would be easier to stay there and use
>space-based materials and energy. Planets are nice places to visit, but not
>necessary as living places.
>
My sentiments exactly!
Shardrukar
writes:
>Personally, I like Robert Forward's comment: "antimatter propulsion is
>no longer science fiction". (Also: "antimatter is easier than fusion".)
>--
Agreed, an awful lot of people seem to place AM in a far future, extremely
exotic propulsion system category. In a beam drive configuration this is
probably more true than not, but AM, and more specifically a-protons, are
extremely useful in several advanced propulsion schemes that could probably be
flyable within a decade or two with the proper funding and mission
requirements.
Gene Nygaard
> No, actually I meant metric tonne. Note the small 'm'
Which goes to show the idiocy of using tons, so ambiguous that you
don't even know if the quantity being measured is mass, force, energy,
volume, power, or whatever else they are used for. Using the word
tonne which is as ambiguous in French as ton is in English is little
improvement (NIST recommends "metric ton" in the U.S.).
The solution is to stick to the SI units. You could have stated it
unambiguously as megagrams (Mg), or better yet 1 Gg (gigagram) for the
number you used) and Erik Max Francis could state his megatons as
teragrams (Tg).
A 1.000 Gg spacecraft travelling at c/2 will have a kinetic energy of
11.23 zettajoules (ZJ).
> "Erik Max Francis" <m...@alcyone.com> wrote in message
> news:3C7C0C79...@alcyone.com...
> > Robert Lynn wrote:
> >
> > > mT is pretty confusing. In SI it is milli Tesla - a magnetic flux
> > > density about 10 times that of the earths magnetic field. It could
> > > also
> > > be a metre Tesla which makes no sense in the context. milli Tonne? =
> > > 1
> > > kg. Mega tonne? = 1000000 tonnes. It seems that you probably mean
> > > metric tonne. In this forum I would forget the 'metric' best to stick
> > > to standard abreviations like kg or Tonnes or lbs.
Using "lbs" for pounds is just as silly as sticking a
language-specific "s" on the plural of SI symbols, which specifically
is not allowed. Just because the rules for English units are no
longer supported and updated doesn't mean you shouldn't use common
sense with them.
> >
> > In context, it was pretty obvious he meant megatonnes, Mt.
> >
> > --
> > Erik Max Francis / m...@alcyone.com / http://www.alcyone.com/max/
Gene Nygaard
John Schilling
>John Schilling wrote:
>> It doesn't matter to you that the passengers and crew of the Slowpoke
>> have needlessly spent 72 years cooped up in a spaceship? Because it
>> will probably matter to *them*.
>> Under your scenario, those same people could just as well have looked at
>> the plans for the Slowpoke, said "we'll wait", spend the next fourty-two
>> years living in a large, diverse, prosperous (inter)planetary civilization
>> instead. And *then* embarked on their interstellar expedition, to spend
>> a mere eight years in transit and begin pioneering their new world with a
>> technology fourty years more advanced.
>> It isn't a competition between the Slowpoke colonists and the Pixiedust
>> colonists. It's a question of whether *any particular* group of colonists
>> should embark on the Slowpoke or wait for the Pixiedust. If the Pixiedust
>> is coming, you wait for it.
>If you foresee the Pixiedust Drive, of course. The odds are of course that
>there won't be an unforeseen breakthrough of that magnitude in that short a
>timeframe. The prospect that there might be is a gamble of course...
If you already *have* the Slowpoke drive, which at 0.05c is unimaginably
and unobtainably fast by present standards, the Pixiedust drive is no
gamble and requires no breakthroughs. Marginal, incremental improvements
in the ability to produce and use energy, a quite ordinary 2.5% annual
growth rate, are all that is required to overtake a 0.05c ship on a
voyage to Alpha Centauri.
--
*John Schilling * "Anything worth doing, *
*Member:AIAA,NRA,ACLU,SAS,LP * is worth doing for money" *
*Chief Scientist & General Partner * -13th Rule of Acquisition *
*White Elephant Research, LLC * "There is no substitute *
*schi...@spock.usc.edu * for success" *
*661-951-9107 or 661-275-6795 * -58th Rule of Acquisition *
Gerry Quinn
>It doesn't matter to you that the passengers and crew of the Slowpoke
>have needlessly spent 72 years cooped up in a spaceship? Because it
>will probably matter to *them*.
I'll bet hibernation works out easier and cheaper than relativistic
travel.
They'll have 72 years in bed, lucky gits.
- Gerry Quinn
Geoffrey A. Landis
>
> No, actually I meant metric tonne. Note the small 'm'
Next time drop the little m; as is obvious, it's confusing, and to the
accuracy of the discussion, it doesn't matter what kind of ton.
--
Geoffrey A. Landis
http://www.sff.net/people/geoffrey.landis
Jack Tingle
> Why, necessairily? Those born there don't 'know what they're
> missing,' so to speak. Even the volunteers probably come, not directly
> from Earth, but from planetary surface, and free-fall space colonies
> that aren't *too* different from this starship.
[snip]
> But after several generations of shipboard travel (assuming they stay
> socially functional...that's my problem), I can't help wondering how
> well they'd *re*adapt to what we consider normal life within a solar
> system...
I've always assumed that the bulk of interstellar space colonists (if
such ever exist :) ), will probably be looking for attractive asteroid
belts and the equivalent of the moons of Saturn, not some overheated,
grubby, oxygen-covered, life-bearing world. I suspect such worlds
will be viewed as interesting curiosities by the colonists who inhabit
systems with them. After all, they don't need to be close to the sun
for power (they have cheap fusion power or better). They just need a
star to anchor them in orbit for convenience, and deep gravity wells
are a nuisance. They might want a nice reservoir of biological
material handy, but that's probably about all.
It might be valuable as vacation homes, though: "Visit exotic,
life-infested terrain; see psuedo-mice and proto-trees! Wildlife like
stoats, voles, sparrows, and the giant opossum, all within your view
at once! Plants of all types all around! Walk outside on a planetary
surface WITHOUT BREATHING GEAR! Swim in SALTY water with little wormy
creatures and fishy-things all around you! Weather, waves, and
nightly luaus! Attractive vacation packages for the adventure tourist
starting a $3000! Orbital telepresence packages much less! Also ask
about our sungrazer packages for a hot time in the old habitat!"
Our descendants who move to other star systems will probably have
attitudes shaped, as you say, by the voyage, not by the assumptions of
the people who started the voyage.
The nice thing about this attitude is that _any_ star system becomes
colony fodder, not just ones with habitable planets. Perhaps
habitable planets are really irrelevant in the long run.
Regards,
Jack Tingle
TomKalbfus
>no longer science fiction". (Also: "antimatter is easier than fusion".)
>
Is antimatter easier than Fusion? Suppose we spent equal amounts of effort
trying to produce and store antimatter as we do in trying to build a fusion
rocket. Which will come first?
TomKalbfus
>space-based materials and energy. Planets are nice places to visit, but not
>necessary as living places.
>
It might not be possible to turn the Ship around and head back to Earth. A
starship would posses enough fuel to come to a stop once it reaches it's
destination, but it wouldn't have enough fuel to accelerate again toward the
Earth and decellerate upon approach.
David Johnston
> and unobtainably fast by present standards, the Pixiedust drive is no
> gamble and requires no breakthroughs. Marginal, incremental improvements
> in the ability to produce and use energy, a quite ordinary 2.5% annual
> growth rate, are all that is required to overtake a 0.05c ship on a
> voyage to Alpha Centauri.
Our planes aren't improving that fast. Why would their spaceships?
Shardrukar
writes:
>Actually, we do, it's been demonstrated. Some years ago, you could buy
>little sealed glass globes, maybe 15cm in diameter, containing plants and
>small shrimp. All you had to supply was light. Many of them died off
>quickly after being sealed up, and a good many more would eventually
>deteriorate in some way or other... but some of them kept going seemingly
>indefinitely, through many generations of plants and shrimp. I don't know
>if there are any still around.
>
Yeah, I've got a 50cm model thats still alive after almost a decade now. There
isn't a tremendous amount of diversity, and I occassionally have to closely
monitor and adjust the amount of light it gets, but, they are very interesting
"models" for habitat enthusiasts.
Gerry Quinn
>Our species seems inclined to conflict. Long lifespans wouldn't help if
>the ship were wrecked by war. I wonder if it'd be possible to genengineer
>a population with lower testosterone levels.
Nuns in Space!
-Gerry Quinn
Jason Goodman
> No, actually I meant metric tonne. Note the small 'm'
small 'm' means 'milli-'. A millitonne is a funny way of saying a kilogram.
It may seem like we're splitting hairs here, but they're important hairs.
David Allsopp
>David Allsopp <d...@tqSPAMbase.demon.co.uk> writes:
>
>> In article <3C7AB71D...@sff.net>, Geoffrey A. Landis
>> <geoffre...@sff.net> writes
>>>
>>> Gerry Quinn wrote:
>>>>
>>>> Why? We can probably make a fission engine that will go at a few
>>>> percent of light speed,
>>>
>>> No, fission really isn't good enough for interstellar travel-- you
>>> really do want fusion.
>>> [...interesting calculations snipped...]
>>> You really do want fusion, or better, if you can get it.
>>>
>>
>> I recall seeing a comment by some space type saying that what we
>> *really* need is a way to make a spaceship behave like a submarine.
>> A sub moves in a medium, and just needs energy to push against the
>> medium to make itself move. A physics breakthrough that allows us to
>> (say) push against the quantum vacuum would give us a NAFAL drive
>> immediately. This is, of course, a reactionless drive but hey, one of
>> the groups is rasfw...
>
>Such a ``vacuum propeller'' will still require energy to run, because
>it cannot consume any less energy than the increase in the kinetic energy
>of the ship without violating the First Law of Thermodynamics and allowing
>you to construct a perpetual motion machine. Hence, unless you postulate
>that energy is not conserved, or that some sort of ``free energy machine''
>exists, a ``NAFAL'' drive would still require an enormous on-board
>energy-supply to get a ship up to a significant fraction of lightspeed;
>for example, to get up to .9 c requires the ship convert at least 84%
>of its initial mass into energy (i.e., a mass-ratio of about 5.3) ---
>even assuming 100% efficient mass/energy conversion, and a 100% efficient
>NAFAL drive. Real ships and drives with less than 100% efficiency would
>need to convert an even higher fraction of their mass into energy.
>For comparison, a 100% efficient photon drive only needs a mass-ratio
>of about 4.4 to get to 0.9 c --- so ironically, it appears that in this case
>at least, a ``vacuum propeller'' is actually _LESS_ efficient than a photon
>drive !!!
While I'd need to seriously brush up my Special Relativity to double-
check your calculations, isn't there a problem on energy grounds? A
photon drive gives energy to the photons in the drive beam, whereas the
magical vacuum pusher (an elvish housemaid!) presumably just converts
other energy directly into kinetic energy for the ship, with none
carried away by the, erm, exhaust I suppose.
>
>A ``vacuum propeller'' would also requires that an ``aether'' or some other
>form of preferred reference-frame must exist for it to ``push against,''
>or else it again cannot be any more efficient than a photon drive without
>violating the First Law of Thermodynamics and allowing you to construct
>a perpetual motion machine. However, the existence of such a preferred
>reference-frame requires that Einstein's Principle of Relativity must
>be false --- and currently there is absolutely =NO= experimental evidence
>that favors an ``aether'' theory over Special Relativity.
I'm not so sure about the necessity of a preferred frame, but since it
almost certainly violates conservation of momentum I'm not holding my
breath for a quick breakthrough...
>So it seems to me that discovering such a ``vacuum propeller'' would by
>itself be insufficient to solve the problem of interstellar flight ---
>you must also discover a ``free energy machine,'' and show that Einstein's
>Special Theory of Relativity is wrong, first.
I don't *insist* on free energy -- I'll settle for the total mass
conversion reactor... Not all at once, of course :-)
--
David Allsopp Houston, this is Tranquillity Base.
Remove SPAM to email me The Eagle has landed.
Michael J Wise
> Try this, what would a 1 meter/sec^2 acceleration capability achieve?
Lightspeed in ...
3 000 000 / 86 400 = 34.7 days.
Aloha mai Nai`a!
--
"Please have your Internet License http://kapu.net/~mjwise/
and Usenet Registration handy..."
Hop David
Gerry Quinn wrote:
Landis had a starship manned by women. But that was for something like a 40 year trip (IIRC).
I guess you could have an all women multigenerational crew if you used artificial insemination
to maintain the population. It's starting to sound like an Amazon fantasy.
Geoffrey A. Landis
> > >Long lifespans wouldn't help if the ship were wrecked by war. I wonder if
> > >it'd be possible to genengineer a population with lower testosterone levels.
>Gerry Quinn replied:
> > Nuns in Space!
Hop David returned:
> Landis had a starship manned by women. But that was for something like a 40 year trip (IIRC).
"Across the Darkness". It's collected in IMPACT PARAMETER.
In the question-and-answer panel discussion after the AAAS Symposium, I
listed a couple of ideas other than generation ships, including the
all-woman crew concept. The _Guardian_ article gave this the headline
"Star trekkers of the future - women with a sperm bank for next generation"
[article at
http://www.guardian.co.uk/medicine/story/0,11381,651199,00.html ].
Oddly, though, although the women-only-crew concept was the headline,
the actual article didn't mention that idea.
..in other news, I just found posted to the sff.net newsgroup the fact
that MARS CROSSING made the final Nebula ballot. Looks like I'm on my
way to visit scenic Kansas City!
Ian Stirling
>
> BC wrote:
>
>> Try this, what would a 1 meter/sec^2 acceleration capability achieve?
>
> Lightspeed in ...
>
> 3 000 000 / 86 400 = 34.7 days.
Err, you might want to double-check the value of C you are using, as
if it's right, you'r not in the same universe as the rest of us :)
--
http://inquisitor.i.am/ | mailto:inqui...@i.am | Ian Stirling.
---------------------------+-------------------------+--------------------------
The fight between good and evil, an epic battle. Darth vader and Luke,
suddenly in the middle of the fight, Darth pulls Luke to him, and whispers
"I know what you'r getting for christmas!" Luke exclaims "But how ??!?"
"It's true Luke, I know what you'r getting for christmas" Luke tries to ignore
this, but wrenches himself free, yelling "How could you know this?",
Vader replies "I felt your presents" -- The Chris Evans breakfast show ca. 94
Hop David
David Johnston wrote:
> Henry Spencer wrote:
> >
> > In article <3C799AB7...@alcyone.com>,
> > Erik Max Francis <m...@alcyone.com> wrote:
> > >> ...it has been over-taken and established by colonists travelling at
> > >> say 50% light speed.
> > >
> > >This is a common theme in science fiction, but it isn't very realistic.
> > >Travel at 10% is manageable, but hard. Travel at 50% is extremely,
> > >amazingly difficult. Travel at 90% is so flipping hard it's almost out
> > >of the question, even for a type II civilization.
> >
> > We quite routinely do things which our forefathers would have dismissed in
> > similar terms. You are making a standard error: assuming that all really
> > drastic changes have already occurred, so the future will be just a matter
> > of incremental improvements on what we have now. This is a common belief,
> > but has repeatedly proven completely wrong.
> >
>
> It doesn't matter.
>
> Suppose, just for the sake of argument that we launch a colonization ship,
> the Slowpoke, that will take, say, 80 years to reach its destination.
> This is possible because the human lifespan is now something like 160.
> Suppose that 40 years after we launch, we suddenly and unexpectedly
> invent the Van Gelbart Pixiedust drive that moves 10 times as fast.
> Given that it will likely take at least a few years to build the
> Pixiedust I, a ship that will take 8 years to reach the same
> destination will still arrive, say, 30 years before the Slowpoke arrives.
>
> So what? The Slowpoke will still arrive to pioneer a new world. In 30 years
> the Pixiedust colony will be barely getting started. Even if it arrived a
> century early, it would STILL be just barely getting started.
Maybe the Slowpoke is manned by Muslims seeking to spread their faith throughout
the cosmos. And the Pixiedust is manned by Jewish refugees. (you can pick other
conflicting groups). A relatively small 30 year old colony would still be an
unpleasant surprise for the passengers of the Slowpoke.
Shardrukar
(TomKalbfus) writes:
>Is antimatter easier than Fusion? Suppose we spent equal amounts of effort
>trying to produce and store antimatter as we do in trying to build a fusion
>rocket. Which will come first?
>
To my understandings utilizing a-protons in several different propulsion
schemes could be online much sooner than most fusion propulsion schemes.
Of course, the most likely near-term usable system sort of blends anti-matter
and (fission)fusion to achieve its function.
James Nicoll
>
>> Try this, what would a 1 meter/sec^2 acceleration capability achieve?
>
>Lightspeed in ...
>
> 3 000 000 / 86 400 = 34.7 days.
Only in a universe where light creeps at 3,000 km/s rather
than the 300,000 km/s we are lucky enough to enjoy.
A 1 m/s/s ship might be able to reach Alpha Centauri in about
13 years, assuming the exhaust velocity is high enough that nasty mass
ratios don't become an issue.
--
"I think you mean 'Could libertarian slave-owning Confederates, led by
SHWIers, have pulled off a transatlantic invasion of Britain, in revenge
for the War of 1812, if they had nukes acquired from the Sea of Time?'"
Alison Brooks
Jordan179
> ___>We do not even know is a closed ecology is possible on less than a
> planetary scale. 1
(1) - There's no reason to think that the requisite scale is the size
of the modern Earthly ecosphere -- in fact we know that it isn't,
since during the Big Freeze (when the oceans froze over, just before
the Paleozoic Era) the total biomass was probably tiny compared to
what it is today.
(2) - The starship's ecosystem has a _big_ advantage over that of any
planet -- it's being run by sapient beings, who can tweak it back into
balance if it starts to go south.
(3) - The starship's ecosystem does not have to last for billions or
millions or even thousands of years -- it only has to last long enough
for the starship to reach its destination.
(4) - If the starship is _at_ a destination, the ecology no longer
need be "closed" since the crew can bring aboard new feedstocks of the
requisite chemicals, and finally
(5) - The starship's ecosystem need not work as well as that of the
Earth's in producing diversity, evolution, etc. -- all it needs to do
is yield food, air, and water for the consumption of the crew and
passengers.
Sincerely Yours,
Jordan
Jordan179
> Why? We can probably make a fission engine that will go at a few
> percent of light speed, but we have no notion as to whether fusion or
> antimatter will be economically practicable in comparioson, even in a
> thousand years.
Since we _already_ have engineering designs for an (impulse)
fusion-powered starship (as regards the drive system, anyway) and we
already have the physics required to make it possible to build an
antimatter-powered starship (if we can lick the economics of
production and the engineering requirements of storage), your
statement makes about as much sense as someone in 1800 saying:
"Why? We can probably make a fast sloop that can cruise over 10 knots,
but we have no notion as to whether coal- or oil-burning steam engines
will be economically practicable in comparison, even in a thousand
years."
(mind you, in 1800 most people _would_ have said that, because in 1800
humanity hadn't yet realized how fast the rate of progress would be.
We have less excuse now).
> Fission is *simple*. We can imagine a big dirty fission-powered
> ion-drive, built to last. Any tokamak-style fusion engine will be far
> more delicate. Antimatter may be always too expensive.
>
> And the first spacecraft won't carry colonists, unless you count
> machines.
If the ship takes centuries to reach its destination, there is no
reason to assume that the launching _civiliztion_ will be in existence
when it arrives. The only reason I could see for doing this would be
if the launchers believed that they had run up against inexorable
physical limitations and that thus this would be the best ship their
civilization could ever launch.
(which I could see happening, btw, if our civilization stagnated).
Sincerely Yours,
Jordan
John Schilling
If Boeing puts the Sonic Cruiser in service by 2015, then yes, our
planes *are* improving that fast. Private-sector airplanes, at
least; hard to say for sure about government airplanes without
peering into the black world.
Interstellar spaceships have the added advantage, in this context,
of actually *benefitting* from increased speed. Shaving half an
hour of flying time off a trip, doesn't mean much when you have
to spend three hours on the ground before and after anyhow. But
cutting the trip down by *years*, matters.
Henry Spencer
Michael J Wise <mjw...@kapu.net> wrote:
>> Try this, what would a 1 meter/sec^2 acceleration capability achieve?
>
>Lightspeed in ...
> 3 000 000 / 86 400 = 34.7 days.
Nope, c is 300 000 000. Handy rule of thumb: 1G (9.81m/s^2) is roughly
c/yr. (Of course, you need relativistic modifications to that after the
first two or three months.)
--
Many things changed on Sept. 11, but the | Henry Spencer he...@spsystems.net
importance of freedom did not. -SpaceNews| (aka he...@zoo.toronto.edu)
Geoffrey A. Landis
>
> BC wrote:
> > what would a 1 meter/sec^2 acceleration capability achieve?
>
> Lightspeed in ...
>
> 3 000 000 / 86 400 = 34.7 days.
There's an error here, since 1 meter per second^2 is 0.1 G. Since one G
is approximately lightspeed in one year, 0.1 G would be lightspeed in
10 years.
correct calculation:
t = v/a = (300,000,000 m/sec)/(1 m/s^2) = 300,000,000 sec
(not 3,000,000 seconds)
Henry Spencer
Very probably the antimatter. Things might be different if fusion
reactors were off-the-shelf items; then the only problem would be turning
that technology into something workable for a rocket. But the basic
fusion technology doesn't exist yet.
CERN and Fermilab make antimatter now, although in small quantities at
high cost. Much remains to be done in handling technology and in making
production more efficient, but in general there are fewer unknowns.
John Schilling
>David Johnston wrote:
>> John Schilling wrote:
>>>It isn't a competition between the Slowpoke colonists and the Pixiedust
>>>colonists. It's a question of whether *any particular* group of colonists
>>>should embark on the Slowpoke or wait for the Pixiedust. If the Pixiedust
>>>is coming, you wait for it.
>> If you foresee the Pixiedust Drive, of course. The odds are of course that
>> there won't be an unforeseen breakthrough of that magnitude in that short a
>> timeframe. The prospect that there might be is a gamble of course, but a
>> much smaller and more innocuous one than the possibility that when the
>> Slowpoke arrives, there will be some undetected quality about the planet
>> that will wipe them all out anyway.
>Or to put it another way: if you're commuting to work, it's wiser to take
>the bus than to sit at home hoping that someone will land a helicopter in
>your backyard and offer you a lift.
If the bus is going to take *eighty years* to get you to work, the smart
move is to stay home for fourty years, investing what would have been your
bus fare in a decent mutual fund portfolio, and buy your own helicopter.
>And there's another factor to consider: you're considering only one possible
>destination. If a miracle occurs, and the Pixiedust drive is created, a
>smart civilization will send the U.S.S. Pixie off to SOME DIFFERENT STAR
>than the destination of the Slowpoke.
A smart civilization WILL NEVER HAVE SENT the damned Slowpoke. A smart
civilization will understand that the money to pay for a Slowpoke is
better put in escrow to buy a later, faster ship that will accomplish
the same mission sooner.
Gerry Quinn
>Gerry Quinn wrote:
>
>> In article <3C7CF0B3...@tabletoptelephone.com>,
> hops...@tabletoptelephone.com wrote:
>> >Our species seems inclined to conflict. Long lifespans wouldn't help if
>> >the ship were wrecked by war. I wonder if it'd be possible to genengineer
>> >a population with lower testosterone levels.
>>
>> Nuns in Space!
>
> year trip (IIRC).
>I guess you could have an all women multigenerational crew if you used
> artificial insemination
>to maintain the population. It's starting to sound like an Amazon fantasy.
Except Amazons are as bad as Men. It must be Nuns!
Many of them live in enclosed orders from choice. Not so different from
a spaceship.
- Gerry Quinn
Gordon D. Pusch
> BC wrote:
>> Try this, what would a 1 meter/sec^2 acceleration capability achieve?
>
> Lightspeed in ...
> 3 000 000 / 86 400 = 34.7 days.
Sorry, no --- check your units. c ~= 3e8 m/sec, not 3e6 m/sec.
>From v = c*tanh(at/c) for constant proper (i.e., shipboard) acceleration:
v/c | t
=======|==========
0.01 | 34.7 days
0.10 | .95 yrs
0.50 | 5.2 yrs
0.90 | 9.5 yrs
0.99 | 25. yrs
-- Gordon D. Pusch
perl -e '$_ = "gdpusch\@NO.xnet.SPAM.com\n"; s/NO\.//; s/SPAM\.//; print;'
Michael J Wise
> BC wrote:
> > Try this, what would a 1 meter/sec^2 acceleration capability achieve?
> Lightspeed in ...
>
> 3 000 000 / 86 400 = 34.7 days.
Oh good friggin' grief.
300 000 000 / 86 400 = 9.5 years.
Something in the back of my head kept wispering, "You've Skrood Up!"
Shoulda listened a BIT better.
Sorreee.
Jason Goodman
Geoffrey A. Landis wrote:
> ..in other news, I just found posted to the sff.net newsgroup the fact
> that MARS CROSSING made the final Nebula ballot. Looks like I'm on my
> way to visit scenic Kansas City!
Speaking of which, everybody on this newsgroup should go out and buy a copy
of Landis's book. Four-word plot summary: "Shackleton's expedition... on
Mars!" The book is remarkable in its scientific and engineering detail, and
is quite good in the literary arena as well.
I'm surprised the book hasn't been brought up in this group before.
Sci.space.tech readers will find it particularly interesting for its
realistic treatment of Zubrin-esque Mars missions with a focus on potential
problems, rather than the hyperoptimistic "What could possibly go wrong?"
Zubrin attitude. Also, Landis does a great job of coming up with sights and
events which make Mars a far more interesting place place than the typical
"red rocks and dust storms" treament.
My only real complaint with the book was that the plot was sometimes (but
not always!) predictable, and the characterization wasn't polished enough.
By which
I mean that while the people in the story were far from the typical
white-male-scientist-soldiers so often found in hard SF, they seemed carefully
assembled, rather than organically grown.
But these minor problems shouldn't detract from people's enjoyment of the
book, and the ideas within it should help to change the way we view Mars
missions. It fully deserves its Nebula nomination. Good luck, Geoffrey!
Jan Panteltje
>>
>> BC wrote:
>>
>>> Try this, what would a 1 meter/sec^2 acceleration capability achieve?
>>
>> Lightspeed in ...
>>
>> 3 000 000 / 86 400 = 34.7 days.
>
>Err, you might want to double-check the value of C you are using, as
>if it's right, you'r not in the same universe as the rest of us :)